Nephroma Parile

''Nephroma'' is a genus of medium to large foliose lichens. The genus has a widespread distribution. They are sometimes called kidney lichens, named after the characteristic kidney-shaped apothecia that they produce on the lower surface of their lobe tips, which often curl upwards and thus are visible from above. Sterile specimens that do not have apothecia can look somewhat like '' Melanelia'', ''Peltigera'', ''Platismatia'', or '' Asahinea''. Most species grow either on mossy ground or rocks, or on trees.

All species of ''Nephroma'' contain cyanobacteria (in the genus ''Nostoc'') as a photobiont, which allows the organism to fix nitrogen. In some species the cyanobacteria is the sole photobiont, while other species also contain a green alga photobiont (''Coccomyxa'') and the cyanobacteria is restricted to warty cephalodia on the upper or lower surface of the lichen.

Description

Species of ''Nephroma'' have a stratified foliose thallus with a that is well-developed on both the upper and lower surfaces. The fruit bodies (apothecia) are formed on the lower surface of the thallus, which is later curved backward to expose the hymenium (spore-bearing surface). Initially, the ascomata are immersed with a vegetative covering that splits open at later stages of development. In contrast to all other groups of Peltigerales, the asci of ''Nephroma'' have neither a gelatinous coat nor an iodine-positive apical ring. The brown ascospores are elongated, and have a crosswise partition (septa). Reproductive structures called soredia, isidia, or are present in most species.

The lower surface shows important diagnostic features that vary between species. Some species have a thin layer of very short hairs called pseudotomentum, while others have a distinct mat of longer hairs called tomentum. In species like ''N. resupinatum'', scattered white papillae are visible on the lower surface. These features, along with the presence and nature of reproductive structures (soredia, isidia), are key characteristics for species identification.

Chemistry

Species of ''Nephroma'' can contain various triterpenoid compounds that are taxonomically significant and helpful for species identification. Chemical analysis through thin-layer chromatography is sometimes necessary to distinguish between morphologically similar species.

The presence and combinations of specific triterpenoids can be diagnostic. For example, ''N. orvoi'' contains triterpenoids T1, T3, T4, and T6, while the similar-looking ''N. parile'' contains T2, T3, and T5. Similarly, ''N. tangeriense'' contains both zeorin (also known as T3) and dolichorrhizin (T6), while ''N. laevigatum'' in the Nordic region contains only dolichorrhizin.

Some species can only be reliably distinguished through chemical analysis. For instance, ''N. helveticum'' and ''N. tropicum'' are morphologically identical but can be differentiated by their triterpenoid content, with ''N. helveticum'' containing compounds U1 and U2, while ''N. tropicum'' contains U1 and U3. ''N. resupinatum'' is notable for lacking secondary metabolites entirely, which helps distinguish it from similar species.

Photobionts

''Nephroma'' species form symbiotic relationships with photosynthetic partners () that are essential to their survival. All ''Nephroma'' species contain cyanobacteria from the genus ''Nostoc'', which not only provide products of photosynthesis but also fix nitrogen from the atmosphere, making it available to the lichen. Some species, known as , also contain a green algal partner from the genus ''Coccomyxa'', while others () contain only ''Nostoc''.

Research has shown that the ''Nostoc'' partners in ''Nephroma'' fall into two distinct genetic groups that correlate with the lichen's lifestyle. One group is found exclusively in bipartite species that typically grow on tree bark or rocks, while the other group occurs in tripartite species that usually grow on soil or among mosses. This pattern holds true across wide geographic areas – specimens of the same ''Nephroma'' species collected from different continents often contain nearly identical ''Nostoc'' strains. The green algal partners (''Coccomyxa'') in tripartite species show remarkably little genetic variation across different ''Nephroma'' species and geographic regions. These algae are closely related to some free-living species, including certain algae that live within the cells of ''Ginkgo biloba'' trees.

Evolutionary studies have revealed that transitions between bipartite and tripartite forms in ''Nephroma''s evolutionary history were complex events. When a species gained or lost the ability to partner with green algae, it also had to change the type of ''Nostoc'' it associated with, suggesting that these transitions required concurrent changes in both photobiont partnerships.

Species

*''Nephroma arcticum''
*'' Nephroma australe''
*'' Nephroma bellum''
*'' Nephroma cellulosum''
*'' Nephroma expallidum''
*'' Nephroma flavorhizinatum''
*'' Nephroma helveticum''
*'' Nephroma isidiosum''
*'' Nephroma laevigatum''
*'' Nephroma orvoi''
*'' Nephroma parile''
*'' Nephroma resupinatum''
*'' Nephroma rufum''
*'' Nephroma subhelveticum''
*'' Nephroma tangeriense''
*'' Nephroma tropicum''

Evolution and biogeography

A 2011 phylogenetic study of ''Nephroma'' species in Macaronesia (the Azores, Madeira, and Canary Islands) revealed evidence of recent evolutionary radiation and neoendemism in the region. The study found that all five Macaronesian endemic species evolved relatively recently (within the last 19 million years) after the formation of the volcanic islands, rather than being ancient relict species. These endemic species belong to two distinct lineages, each associated with a widespread Holarctic species (''N. parile'' or ''N. laevigatum''). The research suggested that Macaronesia may have served as a source for subsequent colonisation of continental areas, with evidence of recent dispersal events from the islands to Western North America and the Mediterranean Basin. This represents the first documented case of neo-endemism in lichenised fungi from Macaronesia.

Broader evolutionary studies have revealed complex patterns in how ''Nephroma'' species develop and maintain their symbiotic partnerships. While the fungal partners () of tripartite species do not form a single evolutionary group, their photosynthetic partners show strict patterns of association. This suggests that the evolution of different symbiotic forms in ''Nephroma'' was not a simple matter of gaining or losing a green algal partner. Instead, any shift between bipartite and tripartite forms required simultaneous changes in both the green algal and cyanobacterial partnerships.

The genus also shows distinct ecological patterns in its evolution. Species that grow on trees or rocks (epiphytic or lithophytic species) consistently associate with one genetic group of ''Nostoc'' partners, while soil-dwelling species partner with a different group. This pattern holds true across continents, suggesting that these specific partnerships evolved early in the genus's history and have remained stable over long periods. Despite this specialisation in symbiotic partners, the fungal components of ''Nephroma'' species can show considerable genetic variation within species, particularly in temperate regions.

Uses

Several species of ''Nephroma'' are restricted to pristine, old-growth forests, and thus are important indicator species that have already influenced some forest management decisions. ''Nephroma occultum'' is listed as vulnerable in Canada by COSEWIC.

One species of ''Nephroma'' has been found to produce a brown dye, while another is recorded as being used in Scotland to produce a blue dye for wool. ''Nephroma arcticum'' is called ''kusskoak'' by the Yup'ik of Alaska, and it is traditionally eaten after being boiled with crushed fish eggs. A medicinal tea is also made from the lichen, and is reputed to be a powerful medicine to return strength to a person who is in a weak condition. ''N. arcticum'' contains several antifreeze proteins that have been patented by the Dutch multinational corporation Unilever for their ability to modify the growth of ice crystals; these proteins have been used to improve the texture of low-fat ice cream.

References

{{Taxonbar, from=Q951564

Lichen genera
Peltigeraceae
Taxa named by Erik Acharius
Peltigerales genera
Taxa described in 1810